Add Rotation exp/log aliases (fixes #90)

I intend for the geometry classes to have sound foundations while
also being easy to use in the common setting of building trajectories.
Most users won't be invoking methods directly on the geometry classes,
so I took the liberty of keeping technical Lie theory names.

I still like that decision overall, though I'm happy to enhance usability
by providing aliases. In this case, I settled on `fromDouble()` and
`toDouble()` for the `Rotation2d` `exp()`/`log()` functions.

core/src/main/kotlin/com/acmerobotics/roadrunner/Geometry.kt

@@ -79,6 +79,12 @@ data class Rotation2d(@JvmField val real: Double, @JvmField val imag: Double) {
          */
         @JvmStatic
         fun exp(theta: Double) = Rotation2d(cos(theta), sin(theta))
+
+        /**
+         * Alias for [exp].
+         */
+        @JvmStatic
+        fun fromDouble(theta: Double) = exp(theta)
     }
 
     operator fun plus(x: Double) = this * exp(x)
@@ -97,6 +103,11 @@ data class Rotation2d(@JvmField val real: Double, @JvmField val imag: Double) {
      * Get the rotation as a normalized [Double].
      */
     fun log() = atan2(imag, real)
+
+    /**
+     * Alias for [log].
+     */
+    fun toDouble() = log()
 }
 
 /**